A clinical evaluation of the efficacy of scatter reduction by the moving-slit technique for chest radiography will be undertaken. In addition, an optical masking technique for improving x-ray contrast in chest radiography will also be investigated. Both will be compared to conventional chest radiography techniques. Double-blind readings will be used to investigate nodule perception rates as well as image quality (nodule clarity, etc.). The performance characteristics of ideal air-interspace grids will also be investigated, and compared to conventional grid designs.